1. Field of the Invention
The present invention relates to a step motor, more particularly to a step motor having a stator with a separated structure.
2. Description of the Related Art
FIG. 1 shows a conventional step motor, in which magnetic yokes and coil supports of a stator are integrally connected. In more detail, the stator includes at least a pair of magnetic yokes 1, each mounted in opposition to one another one of the magnetic yokes 1 and centered about a motor axis, a pair of coil supports 2 covering respectively outer surfaces of the magnetic yokes 1, and coil members 3 wound respectively around the coil supports 2. Manufacture of the stator involves first assembling the magnetic yokes 1, then placing the assembled magnetic yokes 1 in a mold to form the coil supports 2 using a plastic material. Such a process is complicated and involves high costs. In addition, the mold itself needs to be designed and produced, further increasing overall complexity and manufacturing costs.
FIGS. 2 and 3 show another conventional stator for a step motor, in which magnetic yokes and outer cylinders are integrally formed. In more detail, the stator includes a pair of coil supports 4, a pair of coils 5 wound respectively around the coil supports 4, two pairs of magnetic yokes 6, and a pair of outer cylinders 7 mounted around the coil supports 4. The innermost two magnetic yokes 6 are inserted respectively into the coil supports 4, whereas the outermost two magnetic yokes 6 are formed integrally and respectively with the outer cylinders 7.
Although this structure allows for direct assembly of the stator that does not involve molding processes, since the outermost pair of the magnetic yokes 6 and the outer cylinders 7 have an integral structure, and the resulting cross section of the integrated magnetic yokes 6 and outer cylinders 7 is U-shaped (see FIG. 3), performing drawing processes for forming these integral elements is difficult. Furthermore, finishing processes are typically performed following drawing to obtain a more precise ratio between a sectional area and a length of excitation fingers 601 of the magnetic yokes 6. The integral structure makes the finishing processes difficult to perform.